Certain amine compounds such as TEPAN, a partially cyanoethylated tetraethylene pentamine, have long been used in the propellant industry as bonding agents in composite propellants containing ammonium perchlorate (AP). They greatly improve the mechanical properties of such propellants by chemically bonding AP particles to the binder matrix. TEPAN is also known to facilitate processing relative to other bonding agents since the mix viscosity of the propellant is not increased as much by TEPAN as it is by most other bonding agents. The disadvantage of using amine bonding agents is that ammonia is liberated during the mix and cure cycles due to displacement of ammonia from AP by amine groups in the bonding agent. The amine-ammonium perchlorate reaction requires subsequent ammonia removal from the mix because any residual ammonia will consume part of the isocyanate curing agent and thus interfere with propellant cure.
In a prior, commonly assigned U.S. Pat. No. 4,493,741 entitled "Amine Salts as Bonding Agents", ammonium salt adducts of TEPAN and TEPANOL and their processes for preparation are disclosed. The process for preparation of the adduct of TEPAN comprises reacting a water solution of the selected ammonium salt with TEPAN while stirring at room temperature. Similarly, a TEPAN-glycidol derivative product (TEPANOL) is also reacted with an ammonium salt to form the adduct of TEPANOL. The ammonium salt is selected from ammonium perchlorate (AP), ammonium nitrate (AN), ammonium sulfate (AS), and ammonium formate (AF).
Mechanical properties of a propellant composition, especially strain at maximum stress at -40.degree. C. are substantially improved. The processing time, particularly the mix cycle time is shortened because of the amine salt bonding agent eliminating or minimizing in situ ammonia generation during the incorporation and mixing of ammonium perchlorate into the propellant mix.
As noted in the above described procedure from the prior U.S. Pat. No. 4,493,741 preparation of the amine salts involved solvation of the ammonium salt such as ammonium perchlorate, ammonium sulfate, etc. in distilled water, addition to the polyamine with stirring, and digestion for several hours at 170.degree. C. or above. After these preparatory steps, ammonia and the copious amount of water present had to be stripped off by heat, purge, and vacuum.
An advantage of a more concise method of preparation of adducts of TEPAN and TEPANOL, provided the end products are comparable in quality, is readily recognized.
Therefore an object of this invention is to provide a method for changing the polyamine to the corresponding ammonium salt that reduces the amount of water to be removed from the finished product by a substantial amount.
A further object of this invention is to provide a method which employs the appropriate mineral acid for reacting directly with TEPAN or TEPANOL to yield the corresponding ammonium salt adduct without generation of noxious ammonia fumes.